To make the tartiflette, place the potatoes in a saucepan of cold salted water and bring to the boil. Simmer until tender enough for the point of a knife to slip through. Drain and leave to cool. Carefully scrape off the skins with a knife and cut into 2cm/¾in thick rounds. Set aside.
Place a frying pan over a medium heat and fry the pancetta (no fat is needed). Sizzle and caramelise the lardons on each side.
Add the onion and cook for 10 minutes, or until soft. Add the wine and cooked until reduced. Season with salt and pepper.
Preheat the oven to 200C/180C Fan/Gas 6.
Layer the potatoes in the base of an ovenproof dish. Cover with the pancetta mixture, then add the crème fraîche, spreading out to evenly distribute across the surface. Lay the cheese slices on top and cook for about 20 minutes, or until everything is melted, bubbling and just brown.
To make the endive salad, mix the vinegar and mustard in a salad bowl. Season with salt and pepper, then whisk in the oil. Add the shallot, mix, then add the endive leaves and mix again, making sure each leaf is gleaming with dressing. Finish with a sprinkle of sea salt.
Serve the tartiflette with the endive salad on the side.
